Field of the Invention
The present invention relates to a magnetic-inductive flowmeter (MID) with a measuring tube and at least one measuring electrode, wherein the measuring tube comprises an inflow section and an outflow section, which are spaced to one another in an axial direction of the measuring tube. The measuring tube has at least one opening on its circumferential wall, in which at least one measuring electrode with its electrode head is arranged. A magnetic field is generated via a coil arrangement, which permeates the inside of the measuring tube. Furthermore, the invention relates to a method for such a magnetic-inductive flowmeter.
Description of Related Art
The measuring principle of magnetic-inductive flowmeters is based on the separation of moving charges in a magnetic field. The meteorological basis is formed by a measuring tube of a non-magnetic material, for example, of a non-magnetic metal or of plastic, which is electrically insulated from the measuring fluid on the flow side by an insulating lining and which is permeated by a magnetic field perpendicular to the flow direction generated by the magnetic unit—for example, using coils. If the measuring tube has a measuring fluid flowing through it having a minimum electric conductivity, the charge carriers, ions or charged particles present in the conductive measuring fluid are diverted by the magnetic field. Due to the charge separation, a voltage results at the measuring electrodes arranged perpendicular to the magnetic field and to the direction of flow, the voltage being measured by a measuring device and evaluated as measuring voltage. The value of the measured voltage is thereby proportional to the speed of the flow of charges moving with the measuring fluid.
By using several electrodes, a volume flow can also be determined. Such a measuring device is known from the publication “Electromagnetic flowmeter with Multiple Poles and Electrodes” from Taiichi Tshima et al. from the Proceeding of Instrumentation and Measurement Technology Conference (IMTC/94, 3, May 10 to 12, 1994, pp 1221-1224) in Hamametsu; Japan. This device comprises several coils and measuring electrodes that are arranged in a plane perpendicular to the measuring tube.
A disadvantage of the known measuring unit is that it only allows for imprecise measurement of the speed of flow, in particular in speed distribution that is not rotation symmetrical.